I. Field of the Invention
The present invention relates to an improvement in a semiconductor transducer using monocrystalline silicon and, more particularly, to a compact, highly integrated semiconductor transducer.
II. Brief Description of the Prior Art
In a conventional semiconductor transducer, a plurality of diffusion strain gages which constitute a bridge circuit are formed on a monocrystalline silicon diaphragm to detect a pressure. An output from the bridge circuit is amplified by a differential amplifier which then generates a voltage in proportion to the detected pressure. The composite resistance of the strain gages in the bridge circuit is too large to be neglected as compared with the input impedance of the differential amplifier, so that the gain of the differential amplifier is lowered due to its connection with the bridge circuit. In order to prevent this decrease in gain, conventionally, the input resistance of the differential amplifier is set to be large. Alternatively, for this purpose, a high-input resistance amplifier circuit constituted by a plurality of operational amplifiers is used.
However, when the differential amplifier portion is integrally formed with the strain gages on a single monocrystalline silicon substrate, a large space is required for the differential amplifier portion since it has a high resistance and a complex construction. As a result, a compact semiconductor transducer cannot be prepared.
In addition, since the temperature coefficient of the resistance of a resistor used in the differential amplifier generally differs from that of the strain gage, the gain of the differential amplifier tends to change in accordance with temperature changes in the conventional semiconductor transducer. In order to compensate for the changes in gain due to such temperature changes, a complicated temperature compensator must be used. In addition to this disadvantage, this compensator cannot be operated with high precision in a wide range of temperature changes.